No need to defoliate. Light is passing through no problem. Defoliation is only "neccessary" to help uncover bud sites on a dense plant when no light is penetrating the canopy.
Like this for instance...day 15 in the photo...
You have to work with what you got. I get it 100 believe me. There's not much else you can do though. Just let er grow. A better light will grow a more plush and filled out plant.